Control system for tap changer with vacuum interrupter

ABSTRACT

A control system for a tap changer using a vacuum interrupter. The control system has provisions for monitoring the vacuum interrupter to detect any failure of such interrupter and thus prevent further operation of the tap changer. Should the interrupter fail to open on a tap change, the tap changer motor is reversed returning the changer to the starting position and locking the changer. Should the interrupter be open at the start of a tap change, the tap changer is reversed returning the tap changer to the starting position and then locking the tap changer. In another embodiment, should the interrupter fail to close after a tap change has been initiated, the tap change is completed and the changer locked in that position.

United States Patent [191 Downs et al. 5] May 22, 1973 1 CONTROL SYSTEM FOR TAP 3,628,l28 12 1971 Buhler ..323/43.5 R CHANGER WITH VACUUM 3,319,125 5/1967 Gilker ..317 22 INTERRUPTER Primary Examiner-Robert K. Schaefer [75] Inventors: Clifford L. Downs, Lenox; Richard Assistant Examiner wi1|iam Smith Blackbum, Dalton, both of Mass- Ailvney-Francis X. Doyle and Vale P. Myles 73 Assi ee: General Electric Com an 1 p y 57 ABSTRACT [22] Filed: Apr. 3, 1972 A control system for a tap changer using a vacuum in- PP 240,573 terrupter. The control system has provisions for monitoring the vacuum interrupter to detect any failure of [52] U S Cl 323/43 5 R 307/136 such interrupter and thus prevent further operation of [51] hijcii:JJJiJJJJJJJJ...JJJJiJJJJJJJJJ ;051,14 thetapchanger-Shouldtheinterrupterfailwopenon [58] Field oi Search 307/136 323/43 5 R a tap change, the tap changer motor is reversed 323/43 5 11 A C l 1 returning the changer to the starting position and locking the changer. Should the interrupter be open at the start of a tap change, the tap changer is reversed [56] References C'ted returning the tap changer to the starting position and UNITED STATES PATENTS then locking the tap changer. In another embodiment, should the interrupter fail to close after a tap change 3,436,646 4/1969 Prescott ..323/43.5 R has been initiated, the tap change is completed and 3,602,807 8/1971 Prescott ..323/43.5 R the changer locked in that position. 3,328,696 6/1967 Schunemann ..3l7/22 X 3,622,867 11/1971 Topper ..323/43.5 R 6 Claims, 4 Drawing Figures H. DRIVE M07012 Patented May 22, 1973 3,735,243

3 Sheets-Sheet 1 rc. v| MOTOR 58- M0%R coma! comoz o o 57572 j I Q C O Q 0 O Q CONTROL SYSTEM FOR TAP CHANGER WITH VACUUM INTERRUPI'ER BACKGROUND OF THE INVENTION This invention relates to tap changers and more particularly to a control system for a tap changer to monitor the vacuum interrupter of such tap changer and prevent further operation of the tap changer upon failure of the vacuum interrupter.

As is well known to those skilled in the art, tap changl0 lector contacts from one contact to another contact of a tap winding. Often means are provided usually in the form of mechanical or electrical switches to open the circuit from the moving tap contact to the load so as to prevent arcing between the moving tap contact and the stationary contact of the winding. One such device is described in U.S. Pat. No. 3,524,033 which discloses one form of bypass switch and vacuum interrupter.

In the tap changing devices such as, for example, those shown in U.S. Pat. No. 3,524,033, a vacuum interrupter is used to interrupt the circuit from the movable contact to the load before such movable contact moves away from the stationary contact on the tap winding. Obviously, if the vacuum interrupter should fail to open, arcing will occur between the contacts causing deterioration of such contacts, and possibly short circuiting of the tap changing mechanism. In order toprevent opening of the current carrying contacts of the tap changer in the event the vacuum interrupter should fail, a control system has been devised to detect such failure and prevent the further operation of 40 the tap changer.

It is, therefore, a principal object of this invention to provide a control system for a tap changer which will monitor the vacuum interrupter and prevent tap changing in the event of failure of such vacuum interrupter.

A further object of this invention is to provide a monitor circuit for the vacuum interrupter of a tap changer which includes provision for permitting a second attempt at tap changing in the event of a failure indica tion of the vacuum interrupter.

BRIEF SUMMARY OF THE INVENTION Briefly, in one form, this invention comprises a control system for a tap changer using a vacuum interrupter. The control system includes a monitoring device which monitors the current flow in the vacuum interrupter. When failure of the interrupter is indicated, by current flow or lack of current flow, the control system prevents further operation of the tap changer. A failure counter may be provided which allows a second attempt at operation of the tap changer after a failure indication to assure that such failure indication was not the result of a random electrical transient.

The invention which is sought to be protected will be particularly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention and the manner in which its various objects and advantages are obtained as well as other objects and advantages thereof will be better understood by reference to the following detailed description of a preferred embodiment particularly when considered in the light of the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic diagram of a tap changing circult having a vacuum interrupter and shown utilizing the control system of this invention;

FIG. 2 is a block diagram of one form of control system of this invention;

FIG. 3 is a timing diagram showing the timing relationship of the control signals of the control system of FIGS. 1 and 2, and

FIG. 4 is a block diagram showing a modified form of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT This invention relates to a control system for the tap changer of an electromagnetic induction apparatus and it is particularly shown in the various figures of the drawing in which like numerals will be used to indicate like parts throughout the various views. Particularly, the invention relates to a control system having a means for monitoring the operation of the vacuum interrupter of such tap changer and has provision for preventing further operation of the tap changer when the vacuum interrupter fails.

FIG. 1 shows one form of tap changer using a vacuum interrupter and showing the control system of this invention connected thereto. Considering FIG. 1, a tapped transformer winding 10 is shown having a plurality of stationary tap contacts 12, 14, 16 and 18. A pair of movable tap selector contacts 20 and 22 are shown which cooperate with the fixed contacts 12, 14, 16 and 18. As is shown, the tap selector contacts 20 and 22 are connected through reactor coils 24 and 26 and bypass switches 28 and 30, respectively, to a contact 32 which is connected to a load 34. A vacuum interrupter switch 36 is shunted across the parallel circuit which includes the bypass switches 28 and 30. As is well understood by those skilled in the art, when it is desired to change from taps in the tap changer, for example, from tap 12 to tap 14, the bypass switch 28 will be opened thus shunting the current from contacts 12, 22 through the vacuum interrupter 36 to the load 34. The vacuum interrupter 36 must then be opened prior to the movement of movable contact 22 to prevent current flow through contacts 12, 22 and thus preventing arcing therebetween. After the contact 22 reaches fixed contact 14 then the vacuum interrupter 36 closes to divide the current through the movable contacts 22 and 24. Bypass switch 28 will then be closed relieving the vacuum interrupter 36 of the current carrying duty. The above description is well known, is found in U.S. Pat. No. 3,524,033, and is also clearly shown in the timing diagram of FIG. 3.

Referring now to the timing diagram of FIG. 3, a tap change is initiated at time zero, and the motor starts to operate to make the required tap change. Then, as shown at curve A, the on position switch changes state shortly after time zero as is indicated by the time scale F. The on position switch locks the control sys tem to make the indicated tap change regardless of change in the voltage level which initiated the tap change. Shortly after initiation of the tap change and the change of state of the on position switch, the bypass switch (such as 28) is opened as is shown at 28 on curve B. Shortly thereafter the vacuum interrupter opens as is shown at 36 on curve C. Curve D shows the tap selector operation at 22' which indicates the movement of movable contact 22 from fixed contact 12 to fixed contact 14.

As will be understood, after contact 22 reaches fixed contact 14, then, as indicated in curve C, vacuum interrupter 36 will close as shown at 36". Shortly thereafter, as shown in curve B, bypass switch 28 will close as shown at 28". Then, of course, as indicated in curve A, the tap change is completed and the tap changer drive motor is deenergized.

As will be understood, if the vacuum interrupter 36 fails to open, then movable contact 22 will be carrying one-half the load current and when it leaves fixed contact 12 severe arcing will occur between such contacts and, as is well known, such arcing could causing a short circuit condition within the tap changing mechanism. In order to prevent the operation of the tap changer should vacuum interrupter 36 fail to properly function, the control system of this invention has been provided. The control system is shown in a preferred form in block diagram in FIG. 2 where the motor control 38 is shown connected to the tap changer drive motor 40 in the same manner as shown in FIG. 1. The essential control system of this invention is shown in FIG. 1 as block 42 and the block diagram of that control system is shown in FIG. 2. As is shown in FIG. 2 an on position switch 44 is provided indicating that the tap changer is at rest in a given tap position. This switch initiates a signal into the interlock and seal-in logic circuit 46 thereby committing the control to continue. The tap change signal is provided from the tap change initiator block 48 to the interlock block 46 as shown. The signal from initiator 48 is fed to motor control circuit 38 energizing motor 40 to drive the contacts in the desired direction.

Current sensors are provided for the vacuum interrupter 36 as indicated by the block 52. These current sensors provide a signal if current is flowing in the vacuum interrupter the signal passing through the amplifiers 54 to the gate circuit 56. When the vacuum interrupter 36 opens or is operated, the signal switch shown by block 58 generates a signal which operates the gating pulse generator 60. The gating pulse generator 60 initiates a pulse signal which is shown by curve E at 60' which thereby provides a signal to gate 56 which by means'of failure detection logic 50 may provide a signal to reverse motor control 38. As will be understood, when the vacuum interrupter opens as indicated at 36 in curve C, no current should be detectedby the current sensors 52. Thus no signal will be apparent in the amplifier 54. However, should current be flowing in the vacuum interrupter after the interrupter is supposed to openas shown at 36' in curve C, then a signal will appear through amplifiers 54 and through gate 56 when the gating signal is applied from generator 60. This signal from amplifiers 54 through gate 56 will be applied to the failure detection logic block 50 to thereby reverse motor control 38, thus preventing any movement of the tap changer movable contact 22.

As will be understood, a plurality of gears and cams are provided in the tap changer motor drive system. Thus even though the motor 40 has operated since time zero, at the time of gating pulse 60, tap 22 has not is open at the beginning of the tap change and this would be sensed when the bypass switch was open as at 28'. Obviously, between the time of the opening of 28 and the opening of the vacuum interrupter 36, current should be flowing in the vacuum interrupter. If no current is flowing, then the current sensor will cause a failure signal to be generated causing the motor to be reversed driving the tap changer back to the starting position. This may be obtained, for example, by a current signal storage generator and inverter as indicated at 62 in FIG. 2. When current through the interrupter is detected by current sensors 52 after the bypass switch has opened, then a signal will be stored in the current signal storage 62. After the interrupter 36 opens, the gating signal from generator is provided to gate 56. If no current signal was stored in 62 then a signal is passed through gate 56 to the failure detection block 50. Thus, if there is no current in the vacuum interrupter during the period from 28' to 36 of FIG. 3, then no signal is stored in the current signal storage 62. As will be understood, by use of the storage and inverter 62, if no signal is stored, then the inverter portion will provide a failure signal thru gate 56 when the gating pulse from generator 60 opens gate 56. This failure signal will cause motor control 38 to reverse, then the tap changer will shut down. However, if a signal is stored in the storage and inverter 62, then no signal will be provided when gate 56 is opened.

In order to prevent a random electrical transient from shutting down the tap changer, should it occur at the moment gate 56 is open, a failure counter may be provided in the failure detection logic block 50. This is indicated by counter 64. Counter 64 provides a time delay after the failure detection logic 50 has reversed motor control 38 and the inhibit signal has locked out the interlock logic block 46. After the time delay, the inhibit signal is removed allowing initiator 48 and interlock logic 46 to initiate a second attempt to change the tap. If the attempt is successful, the error was caused by a transient and the tap changer resumes normal operation. If the second attempt is unsuccessful, then a failure of the vacuum interrupter 36 has occurred and the inhibit signal is permanently applied to prevent further operation of the tap changer.

Referring now to FIG. 4, a modified version of the control system is shown. In this version, the failure detection if vacuum interrupter fails to open is exactly the same as in FIG. 2. That is, a current signal from the sensors 52a is fed through amplifier 54a to gate 56a. When the gate signal, generated by switches 58a and generator 60a, opens gate 56a the error signal is fed to the failure detection logic 50a which reverses "motor control 38a and through the inhibit shuts down the tap changer. Obviously, if desired, a failure counter may be provided in logic 50a to prevent transients from shutting down the tap changer as previously described. However, should the vacuum interrupter 36 fail to close, as at 36 in FIG. 3, then an open failure-has occurred. The signal switches 58a provide a signal to the pulse generator 600 on both the opening and closing of vacuum interrupter 36. The second pulse from generator 60a, on the closing of vacuum interrupter 36 is indicated by the phantom pulse 60" in FIG. 3. If no current is present in the vacuum interrupter 36 and thus no signal to gate 56a when the second pulse 60 opens the gate 56a then failure detection logic 50a allows the tap change to be completed and then prohibits further operation of the tap changer.

Of course, it will be apparent to those skilled in the art that many types of electronic circuitry may be utilized in the different blocks of the block diagram of FIGS. 2 and 4. In accordance with the basic features of this invention, it is necessary that a sensing means be provided for the vacuum interrupter, the preferred sensor being a current sensor, to determine whether or not current is flowing in the vacuum interrupter during the periods when the interrupter is required to be open for purpose of the tap changing and during those periods when the vacuum interrupter is required to be closed during tap changing. If such current is not found in the vacuum interrupter, then signals are required to be generated which will prevent the operation of the tap changer thereby preventing the movement of a movable tap from a fixed tap while such taps are still carrying a portion of the load current. Obviously, various changes may be made in the specific features of the device of FIG. 1 or in the various types of elements of FIGS. 2 and 4 and all such changes are considered as fall within the scope of the invention as is set forth in the following claims.

What is claimed as new and which is desired to secure by Letters Patent of the United States is:

l. A control system for a tap changer, said tap changer including a tapped winding with a plurality of fixed tap contacts, a pair of movable contacts movable to contact said plurality of fixed contacts, a vacuum interrupter shunting said movable contacts, and a bypass switch between each movable contact and a load, said control system comprising means actuated by an external source, a logic circuit for operating said tap changer, said means electrically connected to activate said logic circuit, sensing means sensing the operating condition of said vacuum interrupter, said sensing means providing electrical signals to said logic circuit to prevent operation of said tap changer when said vacuum interrupter is inoperative,

2. A control system for a tap changer as set forth in claim 1 in which said sensing means senses failure of said vacuum interrupter to open and provides a signal to said logic circuit to prevent operation of said tap changer.

3. A control system for a tap changer as set forth in claim 1 in which a signal storage and inverter circuit is provided, said sensing means electrically connected to said signal storage and inverter circuit, said sensing means providing no signal if said vacuum interrupter fails to close and said signal storage and inverter circuit providing a signal to said logic circuit to reverse said tap changer and prevent further operation of said tap changer.

4. A control system for a tap changer, said tap changer including a tapped winding with a plurality of fixed tap contacts, a pair of movable contacts movable to contact said plurality of fixed contacts, a vacuum interrupter shunting said movable contacts, and a bypass switch between each movable contact and a load, said control system comprising a logic circuit actuated by an external source to cause operation of said tap changer, sensing means sensing the operating condition of said vacuum interrupter, said sensing means providing electrical signals to actuate said logic circuit to prevent operation of said tap changer when said vacuum interrupter is inoperative.

5. A control system as set forth in claim 4 in which said sensing means is connected electrically to a gate, a switch operated by said vacuum interrupter, said switch operating a pulse generator to provide a gating pulse to said gate, said gate providing a failure signal to said logic circuit if said sensing means senses failure of operation of said vacuum interrupter.

6. A control system for a tap changer, said tap changer including a tapped winding with fixed tap contacts, and a pair of movable contacts, a vacuum interrupter shunting said movable contacts and a bypass switch between each movable contact and a load, said control system comprising means to sense the operation of said vacuum interrupter, a logic circuit to operate said tap changer, and means cooperating with said logic circuit to prevent operation of said tap changer when said vacuum interrupter fails, and a counter provided in said logic circuit, said counter providing a time delay and then allowing further operation of said tap changer after said logic circuit prevents such operation. 

1. A control system for a tap changer, said tap changer including a tapped winding with a plurality of fixed tap contacts, a pair of movable contacts movable to contact said plurality of fixed contacts, a vacuum interrupter shunting said movable contacts, and a bypass switch between each movable contact and a load, said control system comprising means actuated by an external source, a logic circuit for operating said tap changer, said means electrically connected to activate said logic circuit, sensing means sensing the operating condition of said vacuum interrupter, said sensing means providing electrical signals to said logic circuit to prevent operation of said tap changer when said vacuum interrupter is inoperative.
 2. A control system for a tap changer as set forth in claim 1 in which said sensing means senses failure of said vacuum interrupter to open and provides a signal to said logic circuit to prevent operation of said tap changer.
 3. A control system for a tap changer as set forth in claim 1 in which a signal storage and inverter circuit is provided, said sensing means electrically connected to said signal storage and inverter circuit, said sensing means providing no signal if said vacuum interrupter fails to close and said signal storage and inverter circuit providing a signal to said logic circuit to reverse said tap changer and prevent further operation of said tap changer.
 4. A control system for a tap changer, said tap changer including a tapped winding with a plurality of fixed tap contacts, a pair of movable contacts movable to contact said plurality of fixed contacts, a vacuum interrupter shunting said movable contacts, and a bypass switch between each movable contact and a load, said control system comprising a logic circuit actuated by an external source to cause operation of said tap changer, sensing means sensing the operating condition of said vacuum interrupter, said sensing means providing electrical signals to actuate said logic circuit to prevent operation of said tap changer when said vacuum interrupter is inoperative.
 5. A control system as set forth in claim 4 in which said sensing means is connected electrically to a gate, a switch operated by said vacuum interrupter, said switch operating a pulse generator to provide a gating pulse to said gate, said gate providing a failure signal to said logic circuit if said sensing means senses failure of operation of said vacuum interrupter.
 6. A control system for a tap changer, said tap changer including a tapped winding with fixed tap contacts, and a pair of movable contacts, a vacuum interrupter shunting said movable contacts and a bypass switch between each movable contact and a load, said control system comprising means to sense the operation of said vacuum interrupter, a logic circuit to operate said tap changer, and means cooperating with said logic circuit to prevent operation of said tap changer when said vacuum interrupter fails, and a counter provided in said logic circuit, said counter providing a time delay and then allowing further operation of said tap changer after said logic circuit Prevents such operation. 